( ?50 > 
L A Letter from Mr. Anthony van Leeuwen- 
hoek, P. (?(. S. concerning the QrcuUtion ofjthe 
Shod inFijhes^ &c. 
Delft In HolUnd, Augufi 2S, 1708. 
S OME time ago, I viewed the Hearts of feveral 
Fifhes, and particularly that of the great Silver- 
Eel, which I cou’d not be weary of looking on, and 
obferving its motion that lafted near four Hours, after 
"twas out of the Body of the Fifli ; and the rather be- 
caufc that Motion was fo regular ; for when the Blood is 
protruded out of the Heart, it is not brought into the 
great Arteries with the fame fwiftnefs, which in that 
cafe wou’d be over-charged with the great quantity of 
Blood : but the Blood thus coming from the Heart, is 
forced into a little white VelTel, almoft of the Figure of 
a Pear, and which one would take for a kind of a Blad- 
der ; one Orifice of which was united to the great Ar-^ 
tery, and the other to the Heart ; in the latter Orifice is 
a Valve, theufe of which is, that (when the Blood is 
protruded from the Heart into theaforefaid Veffel that 
I deferibed to be like a Pear) it might not run back 
again into it : which Veffel having been cut acrofs, I 
obferved the infide of it to befurnifhed with fo many 
fmall Particles, that ’twas in a great meafure fill’d with 
them ; and thefe internal Particles I conceive to be made,^ 
to the end that wlien the Blood is protruded into the 
Veffel, by dilating and contrading it felf it may pre- 
fently force the fame into^ the Great Artery.. 
.■When 
